P851: ANTIBODY TARGETING OF SOLUBLE MHC-CLASS-I-RELATED MOLECULE AUGMENTS NATURAL KILLER CELL FUNCTION BY RESTORING NKG2D IN MULTIPLE MYELOMA
Authors: Sojeong Kim, Haerim Chung, Chung Hyun Park, Yeonhee Kim, Jennifer Wu, Eui-Cheol Shin, Hyunsoo Cho, Jin Seok Kim
Journal: HemaSphere (2023)

Topic: 13. Myeloma and other monoclonal gammopathies - Biology & Translational Research Background: The human tumor-derived soluble MHC-class-I-related molecule (sMIC) impair lymphocyte cytotoxicity by downregulating NKG2D, which is one of the major activating receptor on natural killer (NK) cells. In this regard, sMIC-neutralizing nonblocking anti-MIC mAb (B10G5) was developed as a strategy to restore NKG2D-mediated antitumor immunity. However, the therapeutic effect of targeting sMIC has not been described in patients with multiple myeloma (MM). Aims: To examine the pre-clinical efficacy of B10G5 in MM Methods: The level of sMIC was examined by ELISA in peripheral blood (PB) and bone marrow (BM) of healthy donor, patients with monoclonal gammopathy of undetermined significance (MGUS), smoldering MM, and MM. The proportion and the immuophenotype of NK cells were analyzed by multicolor flow cytometry in patient-derived BM mononuclear cells (BMMCs). MM and NK cell-lines were employed for analyzing immunophenotype, cytokine secretion, degranulation, and cytotoxicity in the presence or absence of B10G5. Results: The level of sMIC was higher in MM patients compared with healthy, MGUS, and SMM. Indeed, sMICA was higher in BM compared with PB of MM patients. There was a correlation between the level of sMICA and the percentage of plasma cells in BM of MM patients at diagnosis determined by morphology and flow cytometry. Of note, the level of sMICA inversely correlated with the NKG2D+ NK cells among CD56dimCD16+ NK cells in BM of MM patients. The addition of MICA protein in culture of patient-derived BMMCs downregulated expression of NKG2D on NK cells, while the addition of patient-derived BM plasma did not alter NKG2D expression on NK cells. The expression of NKG2D on NK cells was enhanced in the presence of both patient-derived BM plasma and B10G5, while minor changes were observed in other NK activating receptors such as CD226, NKp46, NKp30 and NK inhibitory receptors such as KIR, NKG2A, and TIGIT. The changes in the level of NKG2D expression on CD8+ and CD4+ T cells in BMMCs of MM patients in the presence or absence of plasma and B10G5 were not significant. In vitro, MM cell-lines (RPMI 8226, U226B1, SKO-007) highly and distinctly expressed MICA, while leukemia (IM-9, HS 602) and lymphoma (Jiyoye, Daudi, RPMI 6666, H9, HuT 78) cell-lines did not express MICA. As we were unable to detect endogenous sMIC in the culture soup of MM cell-line, we transduced MICA into the SKO-007 cell-line and generated SKO-007_MICA cell-line to model culture system with sMICA. Co-culture of NK-92_mIL15_CD16 cell-line with SKO-007_MICA in the presence of B10G5 augmented NK cell function compared with the IgG control in terms of cytokine secretion (TNF-α, IFN-g), secretion of perforin, granzyme B, degranulation (CD107a), and apoptosis of MM cells. Summary/Conclusion: The clinical utility of B10G5 may hold promise as a new strategy for myeloma cellular-immunotherapy by augmenting NKG2D on NK cells. Keywords: Immune therapy, Multiple myeloma, Natural killer